1. Field of the Invention
The present invention relates to a six-row ball bearing linear guideway, and more particularly to a ball bearing linear guideway with improved rated static load capacity in the upward, downward and lateral directions.
2. Description of the Prior Art
Ball bearing linear guideway is an important linear transmission device, and has been widely used on different transportation devices because of its advantages of high efficiency and accuracy. Rated static load capacity is an important consideration when choosing ball bearing linear guideways, including the rated static load capacity in the downward, upward and lateral directions. The rated static load capacity of a ball bearing linear guideway is usually in direct proportion to the number of rows of balls and the diameter of the balls. Therefore, increasing the ball diameter or the number of row of the balls is a measure usually taken to increase the rated static load capacity. However, with the continuously increased machines' requirement for rated static load capacity, the rated static load capacity of the existing ball bearing linear guideway is still insufficient and needs to be improved.
FIG. 1 shows a ball bearing linear guideway disclosed in Japan Patent No. 07-035136, which comprises a slider 11 slidably mounted on a rail 12, and four rows of balls 13 disposed between the slider 11 and the rail 12 and symmetrically arranged at both sides of the rail 12. The number of the rows of balls of the ball bearing linear guideway 10 is increased from 2 to 4 as compared with other ball bearing linear guideways, so as to increase the rated static load capacity of the ball bearing linear guideway 10. However, by looking at the arrangements of the four rows of balls 13, we can see that the four rows of balls 13 all come into contact with the rolling grooves in an arc-shaped 45°-45°, namely, a contact angle of the respective balls with respect to the rolling grooves is 45 degrees. Such arrangements at this angle can equally provide load capacities in downward, upward and lateral directions. Furthermore, the ball bearing linear guideway 10 is designed with the same profile factor, so that the structure of the ball bearing linear guideway 10 can equally provide load capacities in downward, upward and lateral directions. However, this design is still unable to provide a rated static load capacity which is great enough to satisfy the machines which require higher load capacities in downward, upward and lateral directions.
FIG. 2 shows a ball bearing linear guideway 20 disclosed in U.S. Pat. No. 6,132,093, which is a conventional technology for increasing the rated static load capacity in the downward and upward directions. The ball bearing linear guideway 10 generally comprises: a slider 21 slidably mounted on a rail 22, and four rows of balls 23 disposed between the slider 21 and the rail 22. Two rows of balls 23 are disposed at the top of the rail 22 to increase the rated static load capacity in the downward direction, and another two rows of balls 23 are disposed at two sides of the rail 22 to increase the rated static load capacity in the upward direction by contact points. However, by looking at the arrangements of the four rows of balls 23, we can see that the two rows of balls 23 at the top of the rail 22 are only capable of bearing the load in the downward direction, but totally unable to bear any load in the upward and lateral directions, while the two rows of balls 23 at two sides of the rail are able to bear the load only in the lateral direction, but totally unable to bear the load in the downward direction. In general, the load capacity cannot be considerably improved in all of the downward, upward and lateral directions. The load capacity might be improved in the downward direction but not in the upward and lateral direction, as a result, the load capacity in general is still not sufficient to enable the ball bearing linear guideway to be applicable to most machines. Furthermore, due to the fact that both the top surface and lateral surfaces of the rail 22 are provided with rolling grooves for reception of the balls 23, the rail 22 must be subjected to a top grinding process and a lateral grinding process, which substantially increases manufacturing cost and reduces manufacturing efficiency. Besides, the two grinding processes have different grinding datum, which may result in position error between the rolling grooves of the top surface and the lateral surfaces, and reduces the accuracy of the ball bearing guideway.
However, increasing the size of the ball bearing linear guideway may increase the load capacity in all of the downward, upward and lateral directions, but the increased size makes the ball bearing linear guideway inapplicable to most machines.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.